The invention relates to a measuring device with an auxiliary electrode, arranged and insulated in a tubular projection on the mantle surface of the casing of a gas-insulated, encased high-voltage conductor. The measuring device forms a high-voltage capacitor of a capacitive voltage divider with the internal conductor of the high-voltage conductor, which is insulated in the casing. The measuring device is also connected with the casing via a low-voltage capacitor, where the auxiliary electrode is connected to a display or measuring device via a measurement connection emerging out of the projection in gas-tight manner, via a passage. The low voltage capacitor is formed from two nested cones having a specific distance from one another, wherein one cone is an outside cone, and the other cone is an inside cone.
Such a measuring device for a gas-insulated, encased high-voltage installation, especially a high-voltage switch gear compressed gas-insulated with SF.sub.6, and encased with metal, is disclosed in DE-AS 23 41 073. With the known measuring device, which functions like a capacitive voltage divider, the voltage of an internal conductor of the encased high-voltage conductor is measured, where the internal conductor is used as part of the high-voltage capacitor. The auxiliary electrode used for this measurement of the applied operating voltage is inserted in a tubular projection of the casing, which in turn is closed off with a cover. The auxiliary electrode has relatively large dimensions, to guarantee measurement accuracy at the operating frequency.
EP 0 134 187 A 3 discloses a measuring device to determine partial discharges in a high-voltage conductor switch with a capacitive voltage divider, wherein inside and outside cones serve to adapt the characteristic impedance of a measurement cable to the measuring device. This is designed to avoid signal reflections at the measurement connection. However, the usual casing projections used with known conductors with measurement covers, demonstrate low inherent resonance frequencies because of their large size. As a result, the upper limit frequency of the voltages to be detected is limited.
The present invention is directed to the problem of developing a measuring device with an auxiliary electrode for measuring voltage in encased, compressed gas-insulated high-voltage conductors that has a high inherent resonance frequency and thus permits a very high upper limit frequency for the voltages to be measured, and also allows measurement of the alternating voltage at the operating frequency.